White House Counsel Donald McGahn and other Trump administration officials have been so vexed by Jared Kushner’s months-long inability to obtain a permanent security clearance that they have hesitated to get involved in other cases with potential problems, several people familiar with the matter said.

The president’s son-in-law and close adviser has been allowed to see materials, including the President’s Daily Brief, that are among the most sensitive in government. He has been afforded that privilege even though he has only an interim clearance and is a focus in the ongoing special counsel investigation into whether the Trump campaign coordinated with Russia to influence the election.

Abbe Lowell, Kushner’s attorney, said in a statement: “I have inquired and been told that there are a dozen or more people at Mr. Kushner’s level whose process is delayed like his; that it is not uncommon for this process to take this long in a new administration (some taking as long as two years); that Mr. Kushner’s will take longer than usual because of the extent of his holdings, travels and lengthy submissions; and that there was no concern about the process or Mr. Kushner’s ability to do his job. This is just the latest in unnamed sources quoting second-hand hearsay concerning Mr. Kushner that, like the others, will be shown to be untrue.”

Those in McGahn’s office, people familiar with the matter said, feel they cannot take action on other people whose background checks have dragged on because they did not take similar steps with Kushner.

Deputy White House press secretary Hogan Gidley, though, disputed that Kushner’s situation affects any others. “This is absolutely not true,” Gidley said in a statement. “The White House treats all security clearances individually, neutrally and equally.”

McGahn and Kushner have clashed repeatedly on a number of topics, though Kushner’s lack of a clearance has been particularly irksome for the White House’s top lawyer and other administration officials in recent months, people familiar with the matter said.

Gidley said: “Don and Jared have had a great working relationship since the campaign and that has continued throughout their time at the White House. Don has no concerns with Jared’s ability to do his job.”

The issue of security clearances burst into the spotlight this week after it was revealed that two ex-wives of White House staff secretary Rob Porter had accused him of domestic violence and relayed those allegations to FBI background-check investigators. Porter, like Kushner, had been operating on an interim security clearance that allowed him to keep his job in the White House.

Porter first told McGahn in January 2017 of problems with his ex-wives, though McGahn has said he did not know specifically of the allegations of domestic violence. Last fall, though, the White House Security Office informed him of the alleged abuse, people familiar with the matter said.

What you need to know about Jared Kushner's ties to Russia. (Thomas Johnson/The Washington Post)

The White House Security Office makes determinations on security clearances, after the FBI provides the findings from its background checks. McGahn, people familiar with the matter said, decided to wait for a final determination and see whether investigators could substantiate the allegations, rather than ousting Porter immediately.

It was not clear to what extent Kushner’s case weighed on McGahn’s mind as he was confronted specifically with Porter’s situation. McGahn told White House Chief of Staff John F. Kelly, and Kelly agreed that Porter — a fierce ally of his — should be allowed to stay on.

Why Kushner, along with dozens of others, continues to lack a clearance remains unclear. For many, there could be innocuous reasons — for instance, that they are getting checked for the first time, or their extensive business and foreign ties take time to explore.

Kushner is a key figure in special counsel Robert S. Mueller III’s investigation. Though Kushner has not been charged with any crimes, his conduct was referenced in former Trump national security adviser Michael Flynn’s guilty plea. Flynn admitted he lied to the FBI about his contacts in December 2016 with Russian Ambassador Sergey Kislyak and indicated that he was acting in consultation with a very senior Trump transition official.

Court papers did not name that official, but people familiar with the matter said it was Kushner. According to one transition team official, Kushner told Flynn that blocking a U.N. resolution on Israel was a top priority of the president-elect.

Kushner also has had to file several updates to his national security questionnaire — the document that serves essentially as the foundation of the security-clearance process. The questionnaire, known as an SF-86, requests voluminous information about a person’s employment history, finances, family, travel and other matters, which the FBI later checks to help determine if a person should be awarded a clearance.

Kushner’s first form, submitted in January, did not list his foreign contacts and got the dates of his graduate degrees and his father-in-law’s address wrong. He submitted an addendum the next day acknowledging that he had foreign contacts and indicating he was willing to detail them. Then in May, he submitted another addendum, detailing more than 100 calls or meetings with representatives of more than 20 countries.

In June, Kushner submitted yet another addendum; this one listed the meeting he attended with a Russian lawyer at Trump Tower whom Donald Trump Jr. believed had damaging information about Hillary Clinton.